Switchgear is a general term referring to switching and interrupting devices and their combination with associated control, metering, protective and regulating devices, and also assemblies of these devices with associated interconnections, accessories, enclosures and supporting structures used primarily in conjunction with the generation, transmission, distribution and conversion of electric power. An integrated assembly of these devices within a metal enclosure is commonly referred to as switchgear. Larger versions of switchgear may be referred to as switchgear or switchboard, and typically consist of a series metal enclosed sections, each providing a distinct function or set of functions, which are linked together in a horizontal manner to form one continuous piece of equipment called a lineup. Smaller versions of switchgear may be referred to as panelboards, power panels, lighting panels, or load centers, and differ in that they are smaller in size and usually linked together in a vertical manner to form one continuous piece of equipment.
Often, power regulating devices are not integrated within the switchgear equipment. There are a wide variety of regulating devices that have been manufactured as stand alone equipment, such as tapped isolation transformers, autotransformers, inductive voltage regulators, capacitors, tuned passive filters and static power converters. Active filter technology such as that described in U.S. patent application Ser. No. 08/315,473 dated Sep. 30, 1994 titled "Active Filter Control" is relatively new and provides enhancements to power quality not found in prior regulating devices. Active filter technology does not draw harmonic current from the source as does the previous static power converters, and does not have the design, performance and physical volume difficulties associated with tuned passive filters. Active filter technology provides higher speed voltage regulation than prior technology, provides faster control of power factor than prior technology, provides active correction of voltage imbalances, and suppresses parallel resonant tank circuits within the power distribution system.
Applying active filter technology to switchgear allows one active filter device to serve multiple loads. Making it an integral part of the switchgear equipment also simplifies installation. The need to run long power, instrumentation, and control cables to a remote location where a stand alone active filter device would be located is eliminated. Associated conduit and/or cable trays and mechanical bracing devices are eliminated. Accordingly, it would be highly desirable to have an active filter device which serves multiple loads from a single location within power distribution switchgear.
Another problem with a stand alone active filter is that the filter requires it's own incoming power protective device in addition to a protective device on the upstream branch feeder. Also, a stand alone active filter may include a dedicated network gateway which provides it's own network communication protocol rather than utilizing the switchgear network gateway which provides a common network communication protocol used by components within the switchgear. A stand alone active filter thus requires duplicative components thereby increasing manufacturing costs and decreasing overall reliability and efficiency. Accordingly, it will be appreciated that it would be highly desirable to have an active filter device that does not require duplicative components and can be used in a switchgear lineup.